code: def test_struct_dtype_fields(fields):
      fields = {
          "a": "int32",
          "b": StructDtype({"c": "int64", "d": "int32"}),
      }
      dt = StructDtype(fields)
      assert_eq(dt.fields, fields)
  
imports: import numpy
  import pandas
  import pyarrow
  import pytest
  import cudf
  from cudf.core._compat import PANDAS_GE_150
  from cudf.core.column import ColumnBase
  from cudf.core.dtypes import CategoricalDtype, Decimal32Dtype, Decimal64Dtype, Decimal128Dtype, IntervalDtype, ListDtype, StructDtype
  from cudf.testing._utils import assert_eq
  from cudf.utils.dtypes import np_to_pa_dtype
label_desc: Use image node_id 9 for calling a global function with example usage: test_struct_dtype_fields(fields) without return types